Linux is an open-source operating system kernel. A "distribution" or "flavor" of Linux is an operating system built around the Linux kernel, often including additional software, a package management system, and a desktop environment to create a complete, user-friendly operating system. - Ubuntu: A very popular and user-friendly Linux distribution. - Gentoo: A highly configurable Linux distribution that compiles software from source code. - Fedora: A community-supported distribution sponsored by Red Hat, often seen as a testing ground for new technologies that eventually make their way into Red Hat Enterprise Linux.